Why is my “80 Acres” really only 79 acres?

When the original governmentsurveyors began the task of laying out (surveying) the public lands ofOklahoma, one of their instructions was to make each section as close to 640acres as possible.

excerptfrom the BLM manual of Survey Instructions

Chapter 1-21. The basic provisions requirethat the public lands "shall be divided by north and south lines runaccording to the true meridian, and by others crossing them at right angles, soas to form townships six miles square;" that "the townships shall besubdivided into sections, containing as nearly as may be, six hundred and fortyacres each;" and that "the excess or deficiency shall be speciallynoted, and added to or deducted from the western and northern ranges ofsections or half-sections in such townships, according as the error may be inrunning the lines from east to west, or from south to north." The systemof rectangular surveys fits the basic requirements to the curved surface of theglobe.

To obtain 640 acres, they wouldattempt to make the sections 80 chains in length on each side. One (1) chainequals 66 feet so 80 chains equals 5280 feet. A section that is exactly 5280feet square would contain 640 acres.

(5280’x 5280’=27,878,400 squarefeet/43,560=640 acres)

The curvature of the earth didnot allow for the north side of the section to be the same width as the southside of the section, typically resulting in a distance of less than 80 chains.(Click here to read more about Oklahoma Land Descriptions)

Surveying in the late 1800’s in Oklahoma was also not awalk in the park. Distractions such as hostile native Americans, rough terrain,inclimate weather and distance measuring equipment that was somewhat lacking,all led to less than perfect results across various parts of Oklahoma.

The compasses used by early surveyorswere fairly accurate devices and produced some results that would rival modernsurvey methods. The Gunter chain used to measure distances, was not as precise,especially across rough terrain with much elevation differences. Don’t get mewrong, they did a great job with what they had to work with.

Curvature of the earth, less thanperfect measurements in the original surveys, better measurement techniquesused today and corner monuments that have since been replaced, account for manysections that do not (likely never did) contain 640 acres EXACTLY.

Subsequently, the originalsurveyors divided these sections into portions which contained an aliquot partof the original acreage, whatever that might have been.

For example a Quarter Section iscommonly believed to contain 160 acres. Half of that is sometimes referred toin the vernacular as “an 80”. If the original section was, in fact 5280 feetsquare the subsequent “Quarter” section would have been 160 acres but what ifit only really contained 635 acres? The quarter section would then only contain158.75 acres and the resulting “80” would really only contain 79.38 acres.

A lot of deeds were written through the years with theacreage being reported on hypothetical measurements and not actual measurements.So if you have a deed that states “…contains80 acres more or less”, you should not rely on that acreage unless it hasbeen surveyed and confirmed by a Professional Land Surveyor